Various muscle assistance devices have been proposed as can be found in Japanese patent laid open publications No. 2003-250844 and No. 7-163607, for instance, for the purpose of providing an assisting force to the movement of the leg by using a torque actuator consisting of an electric motor or the like attached to a side part of the hip or knee joint. For instance, such a muscle assistance device enables a person caring a bedridden person to produce a force of the leg which is substantially greater than that the person is normally capable of producing or a person having a walking impediment owing to aging or the like to walk on his or her feet.
In the power assist devices disclosed in these Japanese patent laid open publications, the thigh of the user is secured to a rigid thigh support member in the form of an exoskeltal beam by a fastening belt which is connected to the thigh support member and wrapped around the thigh of the user. The leg of the user is similarly secured to the leg support member.
In Japanese patent laid open publication No. 2003-250844, the movement of the thigh of the user is detected by using a sensor provided between the belt fastener for securing the thigh to the thigh support member and the front surface of the thigh and other sensors that are provided in the toe and ankle. The drive force of the torque actuator is controlled according to the output electric signals of these sensors so as to assist the flexing movement of the thigh.
However, according to this prior art, the force sensor is provided between the thigh and the fastening belt wrapped around the thigh. Therefore, the belt has to be securely fastened around the thigh for an accurate measurement, but this prevents free movements of the muscles of the thigh, and causes a discomfort to the user. This prior art also includes force sensors placed under the sole of each foot, but these sensors provide limited information for the control of the walking assistance device.
Also, the fastening belt is intrinsically pliant and flexible, and this is advantageous as it can readily conform to the thigh which may differ significantly from one person to another, but the fastening belt is not capable of uniformly transmitting the force from the thigh support member to the thigh. Typically, the transmitted force concentrates at the point of connection between the fastening belt and thigh support member so that the adjacent part of the thigh is subjected to a localized force, and this is detrimental in transmitting a large force to the thigh and preventing discomfort to the user.
Also, the fastening and unfastening of such a belt is not convenient particularly because the fastening belt must be tautly applied to the thigh of the user and this requires a significant amount of effort.